Method and apparatus for concentrating an aqueous suspension of microalgae

Abstract

The invention relates to a method and apparatus for concentrating an aqueous suspension of microalgae. The suspension of microalgae is passed through a tangential filtering device for partially removing water from the suspension without rupturing the microalgae, thereby obtaining a concentrated suspension of microalgae and filtered water. Such a method can be use in systems for production of microalgae. An apparatus for carrying out the method according to the invention is also disclosed.

What is claimed is:  
     
         1 . A method of concentrating an aqueous suspension of microalgae, comprising the step of passing said suspension through a tangential filtering device to partially remove water from said suspension without rupturing said microalgae, thereby obtaining a concentrated suspension of microalgae and filtered water.  
     
     
         2 . A method according to  claim 1 , wherein the suspension prior to being concentrated has a concentration ranging from 1 to 500×10 6  cells/mL.  
     
     
         3 . A method according to  claim 2 , wherein the concentration of said suspension ranges from 1×10 6  to 50×10 6  cells/mL.  
     
     
         4 . A method according to  claim 1 , wherein the concentrated suspension obtained has a concentration ranging from 2 to 30×10 10  cells/mL.  
     
     
         5 . A method according to  claim 4 , wherein the concentration of said concentrated suspension ranges from 2×10 6  to 10×10 10  to cells/mL.  
     
     
         6 . A method according to  claim 1 , wherein the concentrated suspension obtained is from 2 to 1000 times more concentrated than the suspension prior to concentration.  
     
     
         7 . A method according to  claim 6 , wherein the concentrated suspension is from 100 to 800 times more concentrated than the suspension prior to concentration.  
     
     
         8 . A method according to  claim 1 , wherein the microalgae in the concentrated suspension obtained are alive.  
     
     
         9 . A method according to  claim 1 , wherein said tangential filtering device comprises a cartridge containing a plurality of spaced-apart parallel tubular members and wherein said tubular members have porous walls with pores of a predetermined molecular weight cut-off.  
     
     
         10 . A method according to  claim 9 , wherein said tubular members are hollow fibers.  
     
     
         11 . A method according to  claim 9 , wherein the molecular weight cut-off of said pores ranges from 1000 to 100000 Daltons.  
     
     
         12 . A method according to  claim 11 , wherein the molecular weight cut-off of said pores ranges from 5000 to 20000 Daltons.  
     
     
         13 . A method according to  claim 1 , wherein said tangential filtering device comprise a plurality of tangential filtration cartridges arranged in fluid flow communication with one another or in parallel relationship to one another.  
     
     
         14 . A method according to  claim 13 , wherein said tangential filtration cartridges each contain a plurality of spaced-apart parallel tubular members and wherein said tubular members have porous walls with pores of a predetermined molecular weight cut-off.  
     
     
         15 . A method according to  claim 1 , wherein the microalgae are selected from the group consisting of non-motile unicellular algae, flagellates, diatoms and blue-green algae.  
     
     
         16 . A method according to  claim 1 , wherein the microalgae in the concentrated suspension obtained have a lipidic content which is stable for at least 12 days.  
     
     
         17 . A method according to  claim 1 , wherein the microalgae in the concentrated suspension obtained have a phospholipid content which is stable for at least 12 days.  
     
     
         18 . A method according to  claim 1 , wherein the microalgae in the concentrated suspension obtained have a cholesterol content which is stable for at least 12 days.  
     
     
         19 . A method according to  claim 1 , wherein the microalgae in the concentrated suspension obtained have a reproductive potential which is maintained for a period of at least 25 days.  
     
     
         20 . A method of producing a concentrated suspension of microalgae, comprising the steps of: 
 a) providing a reservoir containing an aqueous suspension of microalgae, and a tangential filtering device in fluid flow communication with said reservoir;    b) passing the suspension from said reservoir through said tangential filtering device to partially remove water from said suspension without rupturing said microalgae, thereby obtaining said concentrated suspension of microalgae and filtered water; and    c) recovering said concentrated suspension of microalgae.    
     
     
         21 . A method according to  claim 20 , wherein said method further includes prior to step (c): 
 b′) recycling the concentrated suspension obtained in step (b) to said reservoir and then repeating step (b).    
     
     
         22 . A method according to  claim 21 , wherein step (b′) is repeated until the suspension obtained reaches a desired concentration.  
     
     
         23 . A method according to  claim 22 , wherein the desired concentration ranges from 1×10 6  to 30×10 10  cells/mL.  
     
     
         24 . A method according to  claim 22 , wherein the desired concentration is from 4 to 1000 times higher than the concentration of the suspension used in step (a).  
     
     
         25 . A method according to  claim 24 , wherein the desired concentration is from 100 to 800 times higher than the concentration of the suspension used in step (a).  
     
     
         26 . A method according to  claim 21 , wherein a fresh suspension of microalgae is added into said reservoir during step (b) or (b′).  
     
     
         27 . A method according to  claim 22 , wherein said method is a continuous method.  
     
     
         28 . A method according to  claim 20 , wherein said tangential filtering device comprises a cartridge containing a plurality of spaced-apart parallel tubular members and wherein said tubular members have porous walls with pores of a predetermined molecular weight cut-off.  
     
     
         29 . A method according to  claim 28 , wherein said tubular members are hollow fibers.  
     
     
         30 . A method according to  claim 20 , wherein the microalgae in the concentrated suspension obtained are alive.  
     
     
         31 . A method according to  claim 1 , used in a system for feeding marine organisms.  
     
     
         32 . A method according to  claim 1 , used in a system for producing microalgae as food for marine organisms.  
     
     
         33 . A method according  claim 1 , used in a system for producing microalgae as a health food.  
     
     
         34 . A method according to  claim 1 , used in a system for producing microalgae as a biofuel.  
     
     
         35 . A method according to  claim 1 , used in a system for producing microalgae for pharmaceutical use.  
     
     
         36 . A method according to  claim 1 , used in a system for producing microalgae for extracting and/or isolating bioactive molecules.  
     
     
         37 . An apparatus for concentrating an aqueous suspension of microalgae, comprising: 
 a reservoir dimensioned to contain the suspension of microalgae to be concentrated;    a tangential filtering device in fluid flow communication with said reservoir for partially removing water from said suspension without rupturing said microalgae; and    a pump for passing said suspension from said reservoir through said tangential filtering device, thereby obtaining a concentrated suspension of microalgae and filtered water.    
     
     
         38 . An apparatus according to  claim 37 , wherein said tangential filtering device comprises a cartridge containing a plurality of spaced-apart parallel tubular members and wherein said tubular members have porous walls with pores of a predetermined molecular weight cut-off.  
     
     
         39 . An apparatus according to  claim 37 , wherein said tangential filtering device comprise a plurality of tangential filtration cartridges arranged in fluid flow communication with one another or in parallel relationship to one another.  
     
     
         40 . An apparatus according to  claim 39 , wherein said tangential filtration cartridges each contain a plurality of spaced-apart parallel tubular members and wherein said tubular members have porous walls with pores of a predetermined molecular weight cut-off.  
     
     
         41 . An apparatus according to  claim 38 , wherein the molecular weight cut-off of said pores ranges from 1000 to 100000 Daltons.  
     
     
         42 . An apparatus according to  claim 41 , wherein the molecular weight cut-off of said pores ranges from 5000 to 20000 Daltons.  
     
     
         43 . An apparatus according to  claim 38 , wherein said tubular members are hollow fibers.  
     
     
         44 . An apparatus according to  claim 38 , wherein said cartridge has a feed inlet for receiving the suspension of microalgae to be concentrated, a first outlet for discharging the filtered water and a second outlet for discharging the concentrated suspension of microalgae, and wherein said tubular members define therebetween a space in fluid flow communication with said first outlet, each said tubular member having an inlet in fluid flow communication with said feed inlet and an outlet in fluid flow communication with said second outlet.  
     
     
         45 . An apparatus according to  claim 44 , wherein said second outlet is connected to said reservoir by a first conduit for recycling the concentrated suspension discharged from said cartridge.  
     
     
         46 . An apparatus according to  claim 44 , wherein said feed inlet is connected to said reservoir by a second conduit.  
     
     
         47 . An apparatus according to  claim 44 , wherein said first outlet is connected to a drain by another conduit.  
     
     
         48 . An apparatus according to  claim 46 , wherein said second conduit is provided with a drain for emptying said reservoir.  
     
     
         49 . An apparatus according to  claim 46 , wherein said second conduit is provided with a drain for emptying said cartridge.  
     
     
         50 . An apparatus according to  claim 45 , wherein said first conduit is provided with a flow control device for controlling the flow rate of the concentrated suspension discharged from said cartridge.  
     
     
         51 . An apparatus according to  claim 46 , wherein said second conduit is provided with a flow control device for controlling the flow rate of the suspension passing through said tangential filtering device.